I continually have the error code of 3rd cylinder misfire. I have the XLT 4.0 6 cylinder automatic.

I have replaced all plugs 4 times, wires twice, coil pack, and fuel injectors. The mechanic also did some sort of valve cleaning stating I should no longer have the issue (not going there again).

After replacing "whatever" it'll ride nice for about 500 (maybe less) miles before the check engine light comes back on. Then it really "jerks" while accelerating. I'm at a loss, and apparently the mechanics have no clue as they just replace the newly replaced parts. I'm not a mechanic but can follow instruction pretty good. I just need to know if there are any others out there with the same recurring problem and what the fix may be. Thank you in advance. And this is my first post to FRF.